The present invention relates to a rotary magnetic head device and a rotary transformer used therefor, and more in detail to a rotary magnetic head device and a rotary transformer used therefor utilized in a VTR (video tape recorder), a DAT (digital audio tape recorder), etc.
FIG. 15 is a cross sectional view indicating the principal part of a rotary cylinder in a rotary magnetic head device used heretofore, in which reference numeral 1 is a magnetic head; 1a is a head base; 2 is a rotary drum; 2a is a fixed drum; 3 is a relay plate (rotor side); 4 is a rotor core (hereinbelow called sometimes simply rotor); 5 is a rotating shaft; 6 is a relay plate (stator side); 7 is a coil (rotor side); 8 is a stator core (hereinbelow called sometimes simply stator); 9 is a coil (stator side); 12 is a ball bearing; and 13 is a disc. Here the rotor core 4 and the stator core 8 constitute a rotary transformer.
As it can be seen from the figure, the rotating shaft 5 is supported rotatably by the fixed drum 2a. The disc 13 is secured to the upper portion of the rotating shaft 5 by inserting the latter in the former. The rotary drum 2, to which the magnetic head 1 is secured, is fixed to the disc 13 and the rotor core 4 as an element constituting the rotary transformer is fixed to the lower portion of the disc 13 by adhesion, coaxially with respect to the rotating shaft 5.
On the other hand, the stator core 8 as the other constituent element of the rotary transformer is fixed to the fixed drum 2a by adhesion, etc., coaxially with respect to the rotating shaft 5.
A driving motor is mounted on the lower portion of the rotating shaft 5 (lower portion of the fixed drum 2a) so as to obtain a driving force (rotating force), although it is not indicated in the figure. The electrical connection between the magnetic head 1 mounted on the rotary drum 2 and the rotor 4 constituting the rotary transformer is effected by the contact between a male relay 31 and a female relay 32.
The rotary transformer composed of the rotor 4 and the stator 8 transmits signals between coils by the fact that a number of coils, which is in general equal to the number of magnetic heads 1, are disposed in grooves formed in the surface portions of the magnetic cores constituting the rotor and the stator, which grooves formed in the magnetic core serving as the rotor 4 and the magnetic core serving as the stator 8, respectively, are disposed coaxially so as to be opposite to each other. The interval between the rotor (magnetic core) 4 and the stator (magnetic core) 8, which are opposite to each other, is about 10 to 60 .mu.m.
FIGS. 16A, 16B, 16C and 16D are cross-sectional views of the principal part of the rotary transformer in a state where the rotor core 4 and the stator core 8 constituting it are opposite to each other. FIGS. 16A and 16B show examples, in which approximately cylindrical conductors, on the outer periphery of which insulating films are disposed, such as polyurethane copper wire, are secured in grooves 41 and 81 by using an adhesive 14 in the form of coils 7 and 9, respectively. On the other hand, FIGS. 16C and 16D show examples, in which spiral coils 7 and 9 are formed simultaneously directly on core surfaces in a plurality of grooves by sputtering, evaporation, and metallizing, etching, etc., using the photolithographic technique. FIGS. 16B and 16C show examples of coils 7 having a single turn.
In order to connect the beginning portion and the ending portion of the coils 7 and 9 with the relays described above, etc., it is necessary to draw out the lead portions of coil end portions on the surfaces, which are opposite to the opposite surfaces of the magnetic cores 4 and 8, in some form. FIGS. 17A, 17B, 17C, 17D and 17E are perspective views showing prior art forms of such a lead portion.
FIG. 17A is a perspective view showing an example, in which the starting lead portion 7a and the ending lead portion 7b of the coil 7 are drawn out on the surface on the opposite side, utilizing a throughhole 401 disposed in the groove 41 formed in the magnetic core 4 for a plurality of turns of the coil 7 indicated in FIG. 16A. It will be recognized that both the starting lead portion 7a and the ending lead portion 7b are inserted in the same hole 401.
FIG. 17B relates to the coil 7 having a single turn indicated in FIG. 16B and represents an example, in which throughholes 401a and 401b are formed independently at end portions of the groove 41 and the starting lead portion 7a of the coil 7 is inserted in the throughhole 401a, while the ending lead portion 7b is inserted in the throughhole 401b.
FIG. 17C shows an example, in which two throughholes 401a and 401b are formed in the groove 41 for the coil 7 having a single turn and the starting lead portion 7a and the ending lead portion 7b are so arranged that they are inserted in the throughholes 401a and 401b, respectively.
FIG. 17D shows an example, in which, for a coil having a plurality of turns indicated in FIG. 16A, no throughholes are formed to be utilized, but a groove 410 for drawing out a lead is formed in the coil groove 41 on the magnetic core 4, the starting lead portion 7a and the ending lead portion 7b being drawn out by means thereof.
FIG. 17E shows an example, in which the spiral coil 7 formed simultaneously in a plurality of grooves by metallizing, etching, etc. using sputtering, evaporation and the photolithographic technique is arranged so that it is drawn out through two throughholes 401a and 401b formed in the neighborhood of the groove 41, the starting lead portion 7a and the ending lead portion 7b being drawn out separately through the throughholes 401a and 401b, respectively, and the lead portions are formed at the same time as the formation of the coil 7.
FIGS. 18A, 18B and 18C are schemes representing a related art example of the rotor core of the rotary transformer having the coil arrangement indicated in FIG. 17A, FIG. 18A being a plan view; FIG. 18B being a cross sectional view; FIG. 18C being a back view thereof. In these figure, reference numeral 4 is the core; 40 is a positioning groove; 42 is a groove for a short ring; 41, 43, 44 and 45 are coil grooves; and 401 and 403 to 405 are throughholes. All the throughholes 401 to 405 pass through from one side of the core 4 to the other and it is a matter of course that the starting and the ending lead portions disposed in the coil grooves 41, 43, 44 and 45 are led to the other side of the core 4 through the throughholes stated above to effect required electric connections.
FIGS. 18D, 18E and 18F are schemes representing a related art example of the stator core of the rotary transformer corresponding to the rotor core shown in FIGS. 18A to 18C, FIG. 18D being a plan view; FIG. 18E being a cross sectional view; FIG. 18F being a back view. In these figures, reference numeral 8 is a core; 80 is the positioning groove; 82 is the groove for a short ring; 81, 83, 84 and 85 are the coil grooves; and 801 and 803 to 805 are the throughholes. The stator core is almost identical to the rotor core in its construction and action.
FIGS. 19A, 19B and 19C are schemes representing another related art example of the rotor core having the coil arrangement indicated in FIG. 17B, FIG. 19A being a plan view; FIG. 19B being a cross sectional view; FIG. 19C being a back view. Here an example is shown, in which two sets of throughholes 401a and 403a to 405a, and 401b and 403b to 405b, are disposed as indicated by suffixes a and b and the starting lead portions and the ending lead portions are led to the other side of the core through separate holes to effect required electric connections.
FIGS. 19D, 19E and 19F are schemes representing another related art example of the stator core corresponding to the rotor core shown in FIGS. 19A to 19C, FIG. 19D being a plan view; FIG. 19E being a cross sectional view; FIG. 19F being a back view. There are disposed two sets of throughholes 801a and 803a to 805a, and 801b and 803b to 805b, which are indicated by suffixes a and b.
FIGS. 20A, 20B and 20C are schemes representing another related art example of the rotor core having a coil arrangement approximately identical to that indicated in FIG. 17E, FIG. 20A being a plan view; FIG. 20B being a cross sectional view; FIG. 20C being a back view. Here an example is shown, in which two sets of throughholes 401a and 403a to 405a and 401b and 403b to 405b, are disposed as indicated by suffixes a and b and the starting lead portions and the ending lead portions are led to the other side of the core 4.
FIGS. 20D, 20E and 20F are schemes representing another related art example of the stator core corresponding to the rotor core shown in FIG. 20A to 20C FIG. 20D being a plan view; FIG. 20E being a cross sectional view; FIG. 20F being a back view. Two sets of throughholes 801a and 803a to 805a, and 801b and 803b to 805b, are disposed, which are indicated by suffixes a and b.
FIGS. 21A, 21B and 21C are schemes representing still another example of the rotor core, in which the coil is arranged as indicated in FIG. 17D, FIG. 21A being a plan view; FIG. 21B being a cross sectional view; FIG. 21C being a back view; in which reference numerals 41 and 43 to 45 and 410 and 430 to 450 indicate coil grooves.
FIGS. 21D, 21E and 21F are schemes representing another related art example of the stator core corresponding to the rotor core shown in FIGS. 21A to 21C, FIG. 21D being a plan view; FIG. 21E being a cross sectional view; FIG. 21F being a back view; in which reference numerals 81 and 83 to 830 to 850 indicate coil grooves.
FIGS. 22A, 22B and 22C are schemes representing still another example of the rotor core, FIG. 22A being a plan view; FIG. 22B being a cross sectional view; FIG. 22C being a back view; in which 401a, and 403a, 403b to 405a, 405b are small holes, which are formed by dividing one throughhole having a diameter of about 1 mm into two holes with a partitioning member 10 made of non-magnetic resin, etc., in order to draw out an uninsulated coil through the same throughhole.
FIGS. 22D, 22E and 22F are schemes representing an example of the stator core corresponding to the rotor core shown in FIGS. 22A to 22C, FIG. 22D being a plan view; FIG. 22E being a cross sectional view; FIG. 22F being a back view; in which 801a, 801b and 803a, and 803b to 805a, 805b are small holes, which are formed by dividing one throughhole into two holes with a partitioning member 10 made of non-magnetic resin, etc.
In the above related art rotary magnetic head devices and rotary transformers used therefor have been described. As literature describing such related art techniques, JP-A-59-78508, JP-A-61-201405, JP-A-62-179107, JP-U-A-62-114868, JP-U-A-54-110723, JP-U-A-58-129620, JP-A-63-80510, etc., can be cited.
In the related art techniques described above, if a lead, whose outer periphery is coated with an insulating film, such as a polyurethane copper wire, explained referring to e.g. FIGS. 16A and 16B, is used as the coil for the rotary transformer, it is possible to draw out the starting extremity and the ending extremity of the lead through the same throughhole 401, as indicated in FIG. 17A. Since the direction of the current flowing through the starting extremity and that flowing through the ending extremity are opposite to each other, the magnetic field components produced around the two leads are canceled by each other so that the sum of them is close to zero and therefore they have no undesirable influence on the coupling coefficient between the coil on the rotor core and the coil on the stator core, determining characteristics of the rotary transformer.
However, in order to fabricate the coil with this insulated coated lead, a number of fabrication steps are necessary. In particular, recently, in a rotary transformer, on which a number of magnetic heads are mounted, in order to meet requirements of high performance in a VTR, etc., there are disposed the same number of coils (tracks) on the rotary core side and on the stator core as that of the magnetic heads and since the number of coils (tracks) disposed in the rotary transformer is increased, a great number of steps are required. For this reason, it is desired to form spiral coils 7 and 9 simultaneously in a plurality of grooves on the cores by sputtering, evaporation, metallization, and etching, etc., using the photolithographic technique, as indicated in FIGS. 16C and 16D.
However, in this case, in order to prevent a short-circuit between the starting extremity and the ending extremity of the uninsulated lead thus formed, it is necessary to dispose a throughhole 401a for the starting lead and a throughhole 401b for the ending lead separately in the coil as indicated in FIG. 17E to draw out the starting and the ending extremity, respectively. In this case, another problem is produced. That is, as described previously, in the case where the starting and the ending extremity of the lead are drawn out through the same throughhole, since the direction of the current flowing through the starting lead and that flowing through the ending lead are opposite to each other, the magnetic field components generated around the two leads cancel each other. On the contrary, in the case where they are drawn out through separate throughholes, the magnetic field components don't cancel each other and therefore they have an undesirable influence as a leakage inductance. For this reason, the coupling coefficient between the coil on the rotor core and the coil on the stator core is worsened and the signal transmission efficiency between the two coils is lowered. In particular, in the rotary transformer in the rotary magnetic head device, on which a number of magnetic heads are mounted, the same number of coils (tracks) as the number of the magnetic heads is disposed so that the interval between two adjacent coils is decreased and the width of the coils (tracks) is also reduced. For this reason, worsening a in the coupling coefficient is significant.
As a related technique for preventing this worsening of the coupling coefficient, that disclosed e.g. in JP-A-63-8050 can be cited. According to this technique, in order to draw out both the starting lead and the ending lead formed by the photolithographic technique through the same throughhole, an insulator is disposed between different coil conductors, which are connected with separate members serving as lead conductors, and these lead conductors are located in the throughhole. By this method, steps of applying the insulator and connecting the coil with the lead conductors were necessary and it was required to connect electrically the lead conductors further with other members at the position, where the lead conductors emerge from the throughhole.
As another related technique, a method is known, by which a hole is divided into two small holes by using a non-magnetic substance and the starting lead and the ending lead are drawn out through the respective throughholes. However, by this rotary transformer, although the worsening of the coupling coefficient is lessened, since the non-magnetic substance disposed in the hole for dividing it has been heretofore a material made of resin having a significant difference in a thermal expansion coefficient from the magnetic substance constituting the cores, when they are heated for sintering, etc. at the fabrication of the coils, it gives rise to stress, which remains in the interior thereof, which gives rise to a problem that cracks are produced in the cores.
Further, in the case where a hole is divided into two small holes, through which the starting lead and the ending lead are drawn out respectively, when the lead itself is formed by sputtering, evaporation, metallizing, etc., the lead is formed on the surface of the material made of resin serving as the non-magnetic substance. Therefore there has been problem that the device was lacking in the reliability from the point of view of thermal influences, resistance against chemical reagents, etc.